Vol. 24, Mo. 8 
Page 5 
Cooperative Waterfowl Research - W-88-R F.C. Bell rose, S.P. Havera, 
- - g.A. Perkins, H.K. Archer 
Flocks of migrating waterfowl winging their way to northern breeding grounds 
are a welcome sign of the return of spring each year. Numbers of ducks in 
Illinois were already on the increase by late February 1981 when Robert Crompton 
made the 1st spring aerial census flight. Duck numbers in the Illinois Valley 
peaked at 206,600 in late February, 40% of the peak for the previous fall of 
1980. In the Mississippi Valley, duck numbers peaked at 398,000 during late 
March, 42% of the fall 1980 peak. These numbers were considerably lower than 
the 1980 spring peak numbers for ducks: Illinois Valley, 1,642,500 (130% of 
fall 1979 peak) and Mississippi Valley, 1,160,000 (80% of fall 1979 peak). 
Peak numbers of 36,000 Canada geese, approximately 600 of which were the 
giant race, and 2,600 snow geese were present in the Illinois Valley during 
February of 1981. The Mississippi Valley hosted peak numbers of 5,300 Canada 
geese and 2,900 snow geese. These peaks for the entire spring migration 
represented only 5-20% of the geese observed in the same locations during the 
I960 spring. 
Waterfowl stay in Illinois for a shorter time during spring migration than 
during fall migration. Goose concentrations decreased abruptly by mid-March of 
1981, and duck numbers were declining rapidly by the 1st of April. Common golden¬ 
eyes and common mergansers, which overwinter in Illinois, are the 1st species to 
depart for the northern breeding grounds. Geese are also early migrants, followed 
by such dabblers as pintails, mallards, black ducks, and wigeon, some of which 
spend the milder winters in Illinois. The majority of the diving ducks arrive 
about midway during the migration season; canvasbacks and redheads are the 1st to 
appear and scaup and ruddy ducks are the last to leave. The latest spring migrants 
are blue- and green-winged teal and northern shovelers. 
Many factors cause the timing and duration of the spring migration to vary 
from year to year: the inconsistency of spring weather (probably the most 
important factor), water levels and food conditions (which are partially dependent 
upon weather), and the physiological readiness of the birds to migrate. 
The unusually mild winter and spring in Illinois in 1980-81 may have allowed 
some waterfowl to winter farther north than normal, thus partially explaining 
the smaller numbers of birds observed in Illinois during spring migration. 
Scarcity of food probably also encouraged migrants to move quickly through Illinois 
rather than concentrate on the rivers and lakes where they could be censused. 
Because fall waterfowl populations are dependent upon the number of breeders 
and breeding ground conditions, the low number of spring migrants is a concern. 
May aerial censuses of the breeding grounds by the U.S. Fish and Wildlife Service 
revealed a decline in breeding numbers of most waterfowl species. Breeding 
numbers of the mallard, the number 1 species of waterfowl harvested in Illinois 
and the Mississippi Flyway, were the lowest censused by the U.S. Fish and 
Wildlife Service since 1962. Because of drought conditions on the breeding 
9 grounds and lower numbers of breeding ducks, we expect to census fewer numbers 
of waterfowl in Illinois this fall. 
